OBJECTIVE: Our purpose was to compare the effect of arginine vasopressin stimulation on platelet free intracellular calcium levels in normal pregnancy, incipient preeclampsia, and established preeclampsia. STUDY DESIGN: Cross-sectional and prospective observational study designs were used, Platelet free intracellular calcium was measured by flow cytometry in 10 nonpregnant female volunteers, 10 women with established preeclampsia and their normal pregnant matched controls, and 64 normal pregnant women at 28 weeks' gestation. All pregnant women were nulliparous. RESULTS: Increased response to arginine vasopressin stimulation was observed in nonpregnant compared with pregnant women (p < 0.001). No differences were observed between women with normal pregnancy, incipient preeclampsia, or established preeclampsia. CONCLUSION: The platelet intracellular free calcium response to arginine vasopressin is not a feature of incipient or established preeclampsia. Therefore, in contrast to a previous report, it does not appear to have value as a predictive test for preeclampsia.